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S SITE HISTORY AND PREVIOUS WORK Previous work at the Site has been performed under the regulatory oversight of the PHS/EHD and the RWQCB and is briefly outlined below: ♦ Removal of underground storage tanks by TVG in 1987. ♦ Installation of six monitoring wells in three phases. • Monitoring wells MW-1,MW-2, and MW-3 (Exceltech, 1987). • Monitoring well MW-4 (Exceltech, 1988). • Monitoring wells MW-5 and MW-6 (WaterWork, 1989). ♦ Quarterly monitoring activities from third quarter of 1989 through second quarter of 1994 (various reports by WaterWork and RESNA, 1989 to 1994). •♦ Groundwater pump and treat system second quarter of 1991 through second quarter of 1994 (various reports by WaterWork and RESNA, 1991 to 1994). ♦ _tSoil and groundwater investigation;in two phases, 1994 and 1995 (RAH Environmental, 1995a&b). w Soil borings SB-1 to SB-7:soil and groundwater sampling. • Hand augered borings HA1 to HA3 within the forklift shop: soil and groundwater sampling. ♦ Additional soil and groundwater investigation 1996 (Draft SECOR report). • SoiI borings SB-8 to SB-10: soil and groundwater sampling. ♦ HLA review SECOR work and recommends additional investigation(HLA,August 1997) ♦ HLA samples monitoring wells and submits results to PHS/EHD (HLA, September,. 1997 ♦ HLA boring permit application and summary of additional work(HILA,November 21, 1997) ♦ PHS/EM (Mary Meays)letter dated November 19, 1997 approved work plan made miscellaneous requests including oxygenate and 1-2 DCA analysis. ♦ January 7, 1998 meeting at county offices of TVG,HLA, and PHS/EHD representatives (Ms. Lagorio and Ms.Meays)to discuss issues. It was collectively agreed that the Site appears to qualify as a low-risk groundwater site and the purpose of the additional work was to collect the remaining additional site data required to submit a no further action request in accordance with Appendix B. The following agreements were reached: • Fractured casing on MW-1 to be repaired and procedures summarized in the closure report. • One soil and one groundwater sample to be analyzed for oxygenates and 1-2 DCA with EPA Method 8260B. • One additional round of quarterly sampling of the wells.. • Miscellaneous data requests (Appendix B)for inclusion in closure request. ♦ On March 27, 1998,HLA performed the approved additional work including: 3 borings, collecting soil and hydropunch groundwater samples. ♦ In June and early July HLA informally discussed with Ms. Logorio and Mr. Infirm the recent results and requested that a teleconference between,PHS/E D, TVG, and HLA take place to discuss the results and additional work to define the lateral extent of the deeper plume. ♦ On July 24, 1998 a teleconference was held with PHS/EHD(Ms.Lagorio and Mr. In.furna), to discuss the recent data suggesting a deeper groundwater plume and additional work to evalute the plumes lateral extent. ♦ August 1998, TVG reports significant financial loss and puts Thornton Plant UST project put on hold. ♦ December 1998,TVG directs HLA to proceed with UST work and HLA submits Work Plan Addendum#3 dated December 22, 1998. ♦ PHS/EHD(Mr.Infurna)letter, dated January 14, 1999, presents miscellaneous comments and requests several additional borings in the former UST excavation location. ♦ At TVGs request, HLA requests, on January 22, 1999, a meeting with PHS/EHD representatives,Ms. Lagorio and Mr. Infurna, and TVG and HLA representatives.